Stencil sheet



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' cil sheets. These cementitious esters are usu- Patented Sept. 23, 1930 PATENT OFFICE rrrrr .fl nnNnsr n ovorNY, or PHILADELPHIA, PENNSYLVANIA STENCIL snnii'r No Drawing! This invention relates to the production of a type or stylus impressible stenei'l'sheet' of improved composition, and to an improved method of making the same. Broadly the obj ect of the invention is to utilize the film forming properties of carbohydrate esters softened or modifiedin a new and novel manner.

The softening or modifying agents are acid free bodies of a Very staple nature and which therefore do not disintegrate the carbohydrate ester; nor do these bodies, themselves, decompose because of oxidation or become rancid.

At least one of the softening or modifying agents is preferably an absorbent of the other, thus preventing the sweating out of the liq-. uid softening agents. This relatively dry absorbent also makes dispersion of'the modifying agents in the cemetitious mass more'thor- ,ough and uniform This and the use of a colloid mill or a high speed mechanical stirring device so subdivides the softening or'modifying bodies and the cementitious mass that the resulting stencil sheet is very pliable and soft and yet of great tensile strength.

My stencil sheets have long keeping qualities and ma be made and kept in a preferred condition or ready use without previous treatment. 'They are neither sticky nor tacky and they may-be relied upon to out easily and sharply with uniform visibility. When written upon, my stencil sheets produce an inklike impression on the backing sheet which may be easily read. 'The prior art shows the use of various carbohydrate esters as the cementitious material in the making of the dry lacquer type of stenally the nitroderivatives of cellulose pyroxylin), or the acetic derivatives of cellulose,

starch, sugar, and various vegetable gums.

The effective modifying or softening agents are usually vegetable oils, fats, and fatty acids. Theseoils, fats and fatty acids tend to oxidize after a time, especially when in thin filmsas in a stencil sheet, and these products become odorousand rancid. The oxidization of the oils changes these to fatty acids. Most of the commercial grades of oils such as are ,u ed, in stencil sheets, as for example, caster Application filed ll'ul; 11, 1928. Serial No. 292,023.

or palm oils contain quantities of free fatt acids when purchased.

It is well known that acids greatly afiect the stability of the nitrocellulose, causing disintegration. While this effect is more pronounced with strong acids which cause comparatively rapid disintegration with the liberation of oxides of nitrogen, even such Weak acids as oleic acid bring about this change over a period of; time. These disintegration prodnets of nitrocellulose in turn react upon an acid such as oleic, causing it to rapidly become My modifying agents contain no free acids and in fact the sodium or potassium soaps'are mildly'alkaline and therefore act to stabilize j the nitrocellulose, thus producing a sheet which can be kept for a longer period of time than has heretofore been possible.

Tofrefer again to the prior art, it will be noted that various preservatives have been suggested but the fact remains that the acids present do the harm. Actual tests have proven that these preservatives cannot prevent the disintegration of the nitrocellulose film so long as these acid bodies are present nor can the preservatives prevent the oxidization of fats and oilswhen in thin films as in a stencil sheet. As a matter of fact, all of the dry lacquer stencils on the open market at present, known to me, are of the nitrocellulose type containing large quantities of fattyv acids.

In the volumes of prior art examined, no stress is made of the need for uniform and thorough dispersion of the modifying mawith the same initial ingredients and proportions relatively useless stencils may be made because of poor dispersion in the starting materials, and, on the other hand, exceptional .results may be had if I properly combined,

. therein.

use of modifying agents ordinarily not suitable because/of sweating out of the film, resulting in sticky and tacky stencil surfaces which clog the type and otherwise are the cause of much annoyance.

A relatively soft variety of cementitious material may be made into a stencil sheet which will cut fairly well when modified with air or gas bubbles thoroughly dispersed This results in the mass of material being broken up into films of infinite thinness which lack toughness, A stencil sheet coated with this composition will be easily impressible. 7

After prolonged experimentation I have found that a stencil sheet can be made which will be very uniform in quality even when made in large commercial quantities and which will have long keeping qualities.

Stable modifying agents which do not disintegrate the nitrocellulose film are of first importance. My preference is for the use of an alkyl ester of oleic acid such as for example ethyl, methyl, or butyl oleate. These alkyl esters of oleic acid can be readily made, have a very desirable softening effect on the cementitious film, are very clear transparent bodies having high boiling points and do not evaporate from the stencil coating. These-esters will not spoil or becomerancid nor will they promote the disintegration of the cementitious material of the stencil. These stencils may therefore be kept in stock in ready to use condition for along period of time.

The alkyl esters of a fatty acid are in themselves not sufficient to produce an ideal stencil sheet. If sufficiently large quantities ity, and a dry surface film free from stickiness. This absorbent should also promote intimate and uniform dispersion. The material should also be stable and have long keeping qualities in the stencil film and should not cause the disintegration of the nitrocellulose.

I have found that the metallic soaps and more especially the metallic soaps of fatty acids to be most suitable for this purpose. Preferably use the dry and substantially pure soaps having only traces of free alkali. \Vhile the potassium soaps give products of a softer nature,.the sodium soaps on the other hand promote better dispersion and are more absorbent for my purpose.

Of the fats and fatty acids the soaps of most any of these will give results, but the potassium or sodium laureateor oleate are to be preferred.

I prefer to use sodium oleate because this material is cheap and provides the necessary softening, absorbent, and dlspersion qualities when .used with my preferred choice of al-V kyl ester of oleic acid, i. e., ethyl oleate.

' I find that the use of an alkyl ester of oleic acid alone without the use of a metallic soap of a fatty acid produces an inferior stencil sheet and as both productsare stable, and inexpensive, and as the soap tendsto stabilize the nitrocellulose film I find it highly desirable touse this combination of compounds. v

I may also use a wax preferably of vegetable origin such as carnauba wax which is previously dissolved in a suitable solvent such as alcohol or ether. Instead of dissolving the wax I find that abetter result is' attained by using a diluent such .as toluol which will when heated with the wax produce a soft modification. This heated wax solution or mixture is added while hot to the other-in gredients and thoroughly beaten or dispersed therein. Other waxes can be used but those that do not form fatty acids are to be preferred. The addition ofa small quantity of this waxy material helps to promote dispersion and to maintain a dry surface free from stickiness. While the use of the wax is not necessary, it is more simple to maintain a soft but dry surface film when it is used.

Rapid and thorough mechanical agitation is necessary for the reasons before stated and because the substantially dry sodium oleate will not be properly dispersed, otherwise. It is probable that the difficulty encountered in endeavorin g to introduce this material into a pyroxylin lacquer solution brings about the thorough, minute, and colloidal dispersion of the modifying agents within the cementitious film when rapidly and thoroughly beaten into the mass. Because of the thorough dispersion and the absorbent effect of the relatively moisture free soap, the ethyl oleate is retained in the stencil sheet.

The use of these modifying materials, the

' alkyl esters of oleic acid and the metallic soaps of fatty acids and the use of these in combination with each other is the most particular improvement I have disclosed in this application.

I/Vhile the use of various carbohydrate esters with the above modifying agents is possible, I do not find any cementitious. ma-

lllf) terial of this type as suitable for my purpose as nitrocellulose (pyroxylin) It should also be noted that the modifiers tives of fatty acid substances.

.In carrying out my invention, the following formula of my preferred form of stencilcomposition is given.

If 1, is desired to purchasaalacquer solution from the lacquer manufacturer, procure a clear lacquer, preferably resin free.

containing from '8 to.12 parts of to second nitrocellulose (pyrox lin) and 92 to 80 parts respectively of suita le solvents and dlluents.

The lac uer manufacturer can also su ply a suitable thinner and about'one half the quantity of this by weight of the lacquer will be needed.

, I, however, prefer to cut my own lacquer because it is't en more readily possible to control the product to the viscosity and percentage of solid nitrocellulose content. The

materials needed are en ii d the parts are by weight th v Parts Pyroxylin (nitrocellulose) 15 to 20 sec.

Smoist) 570 To uol 800 Butanol 1100 Ethyl alcoho1 1100 Butyl acetate 2750 The pyroxylin and toluol are placed into. a suitable stirring-device and the mass is thoroughly and uniformly wetted with the toluol to prepare the nitrated cotton for the action of the solvents. Preferably I add the other may be stored in drums for use as required. The purchased lacquer solution may be substituted for the above solution. This cementitious'mixture will hereafter be referred to as pyroxylin lacquer.

The next step is to introduce the modifying agents, color and further pyroxylin lacquer thinners to produce a colloidal mass properly tempered and dispersed for use as a stencil coating material. t

I preferably provide'a mechanical stirring device of relativelyhigh speed or I may use a colloidniill; The ob ect being to tho roughly incorporate the ingredients togetherand to minutely disperse the modifying agents within the cementitious mass. I

Two formulae are given. No. 1 includes the use of carnauba wax while No. 2 omits this ingredient, The, proportions given are byv weight and are" those I preferably use but.

with thetoluol used to cut it with. I use ordinarily'l part of carnauba wax and 48 No. 1 No. 2

'Pyroxylin lacquer 96 06 thyl oleate 48 48 -Sodium oleate, dry. 5 12 Carnauba wax i Toluol 48 Victoria blue B dye q.s. q.s.

Stir rapidly for 15 minutes and thin with lacquer thinmu' 48 48 Stir some more. The mixture is now ready to be. poured into the coating pan where the yos'hino paper or other porous paper or fabric may be coated, impregnated or sprayed with the material and the excess, if impregnated, removed in any suitable manner as by scraping the sheet By carefully controlling the viscosity of the pyroxylin-lacquer by the addition of suit-. able quantities of say second pyroxylin and making viscosity determinations any material un-uniformity in the stencil product will be avoided.

less expensive as it is higher in inexpensive diluents.

- It will be noted that the lacquer formula I have given need not contain any nitrocellulose plasticizers such as dibutyl phthalate,

diamyl phthalate, tricresyl phosphate, etc.

These are ordinarilyused to soften or weaken 1 the lacquer film itself because the modifying agents are insufiicient-for this purpose'and also to prevent the crystallization of the modifiers within the lacquer film. Various oils, fats and fatty acids combined with nitrocellulose films often crystallize in this manner and makeJthe use of these high boiling mutual solvents necessary. These plasticizers;

often sw'eat out. making the surfaces sticky and make the dispersion of the modifying agents more difficult.

A lacquer thinner formula such as is most suitable is given below. Proportions are by Toluol 65' Benzol 50 Amyl acetate "1-121 15 Butyl acetate 85 Ethyl acetate 100 Ethyl alcohol (G. D. No. 1) ..'.w 50

in the technical effect.

The production 'of the alkyl ester of oleic" acid iswell known. The sodium or potassium oleate may be readily purchased at any general chemical supply source.

When the stencil sheet is first coated and Victoria blue B is used as the dye, the stencil will be almost black in color. As soon'as the solvents dry out (which takes only a few minutes) the product becomes a beautiful transparent and uniformly colored sheet free from the cloudy semi-transparent appearance of stencils made of pyroxylin lacquer including various fats, oils, fatty acids, etc.

The coating is easily removed and the portion so removed produces an inklike copy of the ornamentation produced thereon, thus greatly facilitating the proof reading of.

the work. By supplying a white lithocoated backing board this resultis greatly enhanced. I

The coating mixture produces films very easily displaced and, therefore, for an in-' expensive stencil sheet ordinary porous paper coated. with this mixture on one or both faces can be used. The results" are not so good as where yoshino paper is used, but for autographic work it is more easily written upon and there is an advantage in cost where a large number of stencils are needed to replace other method of duplication as by the gelatine copy method.

'VVhere a reproduction of an electrotype,

etching or body of type is desired, if this relievo block or body be heated the stencil material may be easily displaced with compa atively little pressure. The ethyl'oleate has a pleasant, fruity,

apple like odor, which is very penetrating however, andqthis can be changed by the addition of adesired perfume such as oil of Wintergreen.

Although a preservative is not necessary, however if-desired because of the use of crude materials or for other precautions, a

lose ester and ethyl oleate.

2. An impressible stencil sheet having a porous base and a coating including a cellulose ester, an alkyl ester of olelc acid and a wax. I

3. An impressible stencil sheet having a porous base and a coating including a cellulose ester, ethyl oleate and carnauba wax.

4. An impressible stencil sheet having a porous base and a coating including nitrocellulose, an alkyl ester of oleic acid and a wax. I

'5. An impressible stencil sheet having a porous base and a coating including nitrocellulose and an alkyl ester of-oleic acid.

Signed at Philadelphia in the county of Philadelphia and State of Pennsylvania this 9th day of July A. D. 1928.

' ERNEST E. NOVOTNY. 

